Jet plating of high melting point materials



Nov. 25; 1958 s. H. SMITH ET AL 2,8

JET PLATING OF HIGH MELTING POINT MATERIALS Filed May 2, 1955 Plus Powder 17 16 I2 1/ 1.91!) 20 21 13 32 Water Water t 65 70 49 5550 56 67 6B 7 72 66 7 44: M 57 k 52 Oxygen Plus as r 52 54 53 60 5/ 50 71 j p e Acetylene wt 73 aer INVENTORS GEORGE H. SMITH JOHN E PELTON RICHARD C. ESCHENBACH United States Patent JET-PLATING OF HIGH MEETING-POINT MAE'IERIALS Application May 2,1955, Serial: No. 505,228 '16Claims. cum-s The gpr-esent invention concerns the application of improved surface coatings to objects and particular'lyrtelates tornew'and improved methods of and apparatus'forflame spraying,uwhich are especially advantageous for applying surface coatings of highmelting point materials' to articles.

.For some time now, it has been'commonpracti-ceto provide an object with a protective coating by spraying the object with a melted and atomized material that would .adhere ito a pre-cleaned surface ofthe object. Surface spraying has been accomplished 'by introducing thecoating materiaL-usually inthe formof'a rod, into thezflame ofa gasburner inorder to melt the material and by thereafter projecting the melted material against the surface to be coated by a blast of air or inert gas. Heretofore, such spraying has been practiced most suc cessfully with the'useoflow meltingpoint metals, and

even these-coatings'have not been satisfactory for many applications, for they are usually porous and frequently unevenly distributed. 'As such, they lackmany of the most desired properties'of a good protectivecoatingsuch as for-example, hardness 'for good Wear resistance and imperviousness for corrosion resistance.

The present inventionhasthe general "purpose of overcoming the several limitations mentioned aboveof known surface spraying practices. Among the-more particular Objects are: To make feasible and practicableithe use of higher melting point materials, as well astheusuallow melting point materials for surface coatings. To reduce porosity-in sprayed surface coatings'so as to obtain increased wear and corrosion resistance in such coatings. And to improve hardness and strength characteristics by providing a wider range of available coating'materials.

Still other objects of this invention arez To'provide'a continuous spraying operation utilizing high thrust to propel coating particles against the surface to be'coated. To make practical the use of fuels with lowerflame-temperatures. To maintain the coating'particles at relatively high temperatures during their travel to the surface of the workpiece without harmtothe latter. Andto increase the residence time of the-coatingmaterial in the flame for a longer period-than heretoforepossible.

According to the present invention,there is provided a method offlame-spraying a surface coating on workpieces, which includes bringing the coating material to a high'temperature by introducing a fuel-oxygen mixture under pressure appreciably above atmospheric into aconfined space where "burning is initiated and introducing coating material into the combustion-space, and thereafter propelling the heated particles toward the surface of the workpiece to be coated at temperatures and linear velocities greater than 500 feet'per'second such thatthe particles are atleast at flowing temperature uponimpact by discharging the burning gases through aportion of: theconfined space inwhich such gases are accelerated to exit velocities greater thanZOOO feet per second,- sufficiently .high to impart'such linear velocities 'to the particles. ,fFlowing tcmperlaturel'may :be defined as that temperature, determined bysumming both'the therinal 2 andkinetic energyofthe material, at which the material or, at least, the lowest melting point constituent of such material becomes-plastic. in the use of many coating materials, particularly metal and metal alloys and compounds, -it isimportant to maintain the burning gases composition non-oxidizing and non-decarburizing to the powderin ordertofproduce a'coating of desired quality.

The spraying operation is continuous and,.in the pro ferred practice of this invention, comprises suspending comminuted solid material in a combustible mixture made up of a fuel and. a combustion supporting agent in proportions that avoid an excessive oxidizing and decarburizing atmosphere upon combustion. The combustion supporting agent may be air. but oxygen is;preferred, particularlywhenplatinghigh melting materials because of the higherflame temperatures produced with its 'use. iCoatingmatei-ial maybe introduced into the combustion zone by suspensioneither in the fuel or in the oxygen, or it maybe suspendedin the combustible mixturebefore or even afterlburning is initiated. The high flame temperatures and thejhigh linear velocity of the flame jet essential tosuccessful jet flame coating is obtainedby passing the particle-carrying mixture to a burner of the internal conibustiontype where ignition of the mixture under pressure produces large volumes of flaming combustion gases that are discharged to the outside through a confining passageway that efiects acceleration ofrthe gases toihigh velocities.

The high-temperatures to which the particles can be heated by being entrained'in the combusting mixture and in thejetflame andthe appreciable temperature increase corresponding to kinetic energy expended upon impact of the hig h velocityparticles upon the surface-of the work tObBtOflJtd make it; possible to melt even high melting pointmaterials (or -at least the lowestmelting point constituent of such materials) sufiiciently to insure afirm mechanical bond with the surface of the body to be coated. I'lhehigh"velocity-imparted to the particles at these temperatures causes "them to deform sufficiently .upon 'impact -to weld togetherto other particles in the coating-so as" to form a substantially non-porous coating. Moreover, in the method described above the thermal andkineticcnergy of coating particles is sufiicient so that the surface of the-workpiece need not be heated to high temperatures, as in hard-facing, etc. Consequently, Well bonded,-non-porous coatings can be produced by the practiceofthis'invention without causing major microstructural changes in the workpiece.

These and other features, objects and advantages of this invention will become apparent from the following detailed description of the accompanying drawings, wherein:

Figure 1 [shows a longit'udinal cross-section through, a preferred form of jet flame gun adapted for the practice of this invention; and

Figure 2 is a fragmentary section through a modification'of the gun shown .in Figure 1.

Figure 3 is a longitudinal cross-section through another form of jet flame gun suitable for the practice of this invention.

"The 'met-hodwof theinvention will now be described in detail: in connection with the drawings, which show two embodiments ofsprayguns adapted for the practice of the invention.

With reference now toFigure 1, a spray gun, indicated generally at 10, is shown .employing a throat-combustion burner 11, which-is the type preferred in the practice of the present invention and which is similar in construction and operation to the'burner disclosed in copending application, Serial No. 212,547,. filed by George H. Smith onfFebruary 24, 1951. For purposes of this invention,:a throat-combustion burner may be defined as a throat element constituted by a confined space unconstricted from inlet to outlet wherein a fluid combustible mixture received through such inlet at one end of the confined space is ignited within the passageway, passed through the confined space, and then discharged from the confined space through such outlet at the other end of the confined space as a stream of hot burning gases to produce a flame having a high heat transfer intensity, a high velocity and substantial thrust.

For satisfactory results, it is essential that conditions during combustion be maintained such that K is between 75 and 750 in the equation:

APP?

wherein:

'A,=cross-sectional area of said stream of fluid combustible material at the point of introduction thereof to said confined space, in square inches A =cross-sectional area of said stream of burning com- In detail, gun It) comprises a burner 11 having a hollow cylindrical section 12 tapered at one end toward an integral elongated, centrally bored barrel 13 and open at its other end for the reception of a fuel injector 14 having a central passageway 15 axially aligned with the axis of barrel 13. A threaded mid-section of the injector engages a tapped portion 16 of section 12, the injector being held in preselected axial position in the burner by a lock nut 17.

The injector 14 is stepped at 18 to provide a mixer section 19 of reduced diameter that lies in radially inwardly spaced relation to section 12 and terminates in an outlet 20 opening into the combustion throat 21 constituted by the bore of barrel 13. The mixer 19 is spaced slightly from the tapered end wall of section 12 to provide an annular passageway for fluid flow from the annular space or chamber 22 around mixer 19 into the barrel 13. A fuel feed line 24 is connected with passageway 15 through a lateral port 23, and an oxygen feed line 25 is connected with chamber 22 through a lateral port 26. In order to secure flashback of the flame, which is initially ignited outside the throat, into the throat 21, the minimum diameter of the outlet should not be substantially smaller than 0.02 inch.

Coating material may be introduced into the burner in comminuted form as a suspension in the fuel or in the oxygen or as a suspension in the combustible mixture. In the embodiment shown in Fig. 1, comminuted material is conveyed by a carrier gas, such as hydrogen, into a nipple 27, threadedly received into the head of a centrally open adapter plug 28 that closes'the rear end of passageway 15. The nipple has its rear protruding end adapted to be connected to the source of coating material and has fitted into its forward end a forwardly extending hollow stem 29 that projects into passageway 15 at least beyond the lateral fuel feed port 23 and delivers carrier gas and entrained coating material to mixer section 19.

Fuel and oxygen are supplied to the throat under pressure, preferably at least 15 pounds per square inch gauge. As the particle-carrying fuel enters the combustion throat 21, itmixes intimately with the oxygen in the rear portion of throat 21 to form a stream of combustible mixture which starts to burn soon after mixing, producing large volumes of flaming combustion gases which pass forwardly at high velocities through the unconstricted confined space of the throat and are then discharged from outlet 30 at the mouth of barrel 13 as a flame jet. The coating particles entrained in the combustion gases are then ejected from the gun in a directed flame jet having a high heat transfer intensity, a high velocity and substantial thrust. In order to prevent excessive heating of the barrel 13 during operation, a sleeve 31 is disposed around the barrel in radially outwardly spaced relation to form a water jacket 32 through which cooling water can be circulated via inlet 33 and outlet 34.

Coating material may also be introduced directly into the combustion zone in powder form or in the form of a rod. The latter is illustrated in Figure 2, wherein an elongated rod 40 of solid coating material is introduced through an opening 41 at the back end of the injector 14, extends longitudinally therethrough, and projects from mixer 19 sufficiently forward into the rear portion of throat 21 that its forward tip lies in the combustion zone. The rod is moved positively by any suitable driving means, such as for example, oppositely rotating friction wheels, shown schematically at 42, which engage opposite sides of rod 40. An O-ring 43 serves to seal opening 41.

It will be seen that a spray gun employing a throat combustion type burner has the unique advantage that the path of the particles throughout its passage through the confined combustion and discharge space is not constricted and, consequently, the particles meet no obstructions upon which they might lodge and cumulatively plug the passageway.

In a modified type of spraying gun shown in Figure 3, the burner employed is of the type where combustion occurs internally, in an enclosed chamber, and the flaming combustion gases are discharged from the combustion chamber through a jet nozzle. The gun comprises a combustion chamber Stl formed within a cylindrical shell 51 and a nozzle body 52 welded to the forward end of the shell. The combustion chamber 50 threadedly receives in its rear open end an injector member 53 which has at its end remote from the combustion chamber a tapped bore 54 into which an adapter 55 is threaded. The forward portion of bore 54 is tapered convergently toward a restricted injector throat 56 which forms an entrance into the relatively large combustion chamber 50. The forward parts of the combustion chamber walls converge forwardly toward the throat 57 of a divergent discharge nozzle 58 whose exit passageway flares outwardly and forwardly.

An oxidizing agent such as gaseous oxygen with pow dered coating material suspended therein is injected under pressure, preferably 15 pounds per square inch or more, through throat 56 into the combustion chamber 50 by an injector 59 which is threaded into an oxygen supply duct 49 centrally disposed in adapter 55. Injector 59 projects into the tapered portion of bore 54 in axial alignment with throat 56 and combustion chamber 50 and terminates in a frusto-conical head 60 that is spaced from tapered walls of bore 54m provide an annular passageway 61 for fluid from bore 54 into the throat 56. A fuel such as acetylene is delivered concurrently but separately under pressure, preferably the same pressure as the oxygen, to the combustion chamber through an eccentrically arranged fuel supply duct 62 in adapter 55, the open portion of bore 54, passageway 61 and throat 56. The fuel and coating-particle-carrying oxygen mix intimately together in passing through throat Y56, and the mixture under pressure burns vigorously in combustion chamber 50, producing large volumes of flaming combustion gas which flow at high velocity through the nozzle 58, carrying the coating particles with them. In this way the coating particles are entrained. in the directed flame jet provided by the discharged gases, which imparts high linear velocity to the particles.

terior wall of these members ature.

rough a tube 63 flwhich extends from "a'header'64 througmafsleve 65 "io the adapter 55 where .it registers withj duct 62 The particle-carrying oxygen'issupplied to du'ct"49 through la tube alongside tube 63 and is with duct49. A water 66 which extends from header64 thro ghsleeve'es received inadaptenSS in registry jacket 67 is formed around the combustion chamber 50 and adapter 55 between the exand an outwardly spaced sleeve 68 threaded at its rear end to sleeve65. Cooling water isintroduced into the jacket "67 "through aconduit 69 in header 64, sleeve 65"anddu'ct 70in adapter 55, for circulation through the"jacket "ai'iclducts 71 in nozzle body 52 in order to cool'the conibustio'rfchamber and the nozzle. Outlets 72 are provided for withdrawing the cooling water.

The atmosphere composition, high powder velocity and high powdertemperature requiredby the methodof this invention can be obtained'in the described spray guns by proper control of the operating variablesand by proper proportioning of certain parts of the gun.

There are several factors that control powder temper- Among the more important of these are the nature of the reactants, the fuel-oxygen ratio, the residence time. of the coating powder in the burning gases,

burner cooling losses, the burner to workpiece distance i and powder velocity. Fuels with high flame temperatures, such as acetylene, for example, are desirable and, where permissible, oxygen-fuel ratios that produce maximum flame temperatures should be used. Such ratios may not be used with many coating materials'for reasons set forth below, but are suitable for flame-plating ceramic materials.

The coating powder is dependent upon powder velocity as well as on flame temperature for its thermal energy, for the kinetic energy of the particles is effectively converted into thermal energy upon impact on the workpiece. This is shown in the following table of temperature rise on impact, calculated assuming completely inelastic collision.

-Temperature rise on impact Resultant Theoretical Temperature Increase, F.

Velocity of Powder, ft./sec.

equivalents of the thermal energy imparted by the flame and the kinetic energy of the powder releasedupon impact. Thus, even though an otherwise satisfactory fuel may have too low a flame temperature for low velocity processes, it can now be used successfully in thepresent method because of the additional heat energy added to the coating material upon impact at the high velocities of the present invention.

The nature of the fuel and the oxygen-fuel ratio affect the oxidation potential of the atmosphere, which in turn, affects the composition of the coating. "For example, carbon content of certain tungsten carbide powders as supplied is 4.5% to 5.0% by weight. With an oxyacetylene volume ratio of 1.0, carbon content in the plating was found by combustion analysis to be about 3.0%. At a 1.4 ratio, carbon content was 2.0%, and at a 2.0 ratio, it was 1.3%. Plating quality varied with the carbon content of the coating, as attested by va iations i hard ess i t enes a surfa e pp anq i The effective oxidation'potential, me'asu'redin thisginsta'nceiby decarburization, of various combinations 'of fuel and oxygen is closely related to the amount of oxidants in the hot burning gases. Oxidants, for example, carbon dioxide and water, may be defined for purposes of this disclosure, as substances having oxidizing properties at the operating temperatures. It has been found that when applying a tungsten carbide plating, for example, the fuel-oxygen ratio should be such that less than 67% by volume of oxidations is formed in the reaction carried to completion, i. e. the ratio of the volume of oxidants to the total volume of products produced by the reaction must be less than 67%. It is particularly important to limit the oxidizing potential of the atmosphere in the use of coating materials readily oxidizable at high temperatures, such as metal and metal carbide, boride, nitride and silicide powders. It is clear'that control of the composition of the flame is important in obtaining proper plating qualities.

Various fuels may be used. Acetylene, which has particularly high flame temperatures at fuel-oxygen ratios producing desirable flame compositions, has been found to be especially suitable for use in flame plating. However, other fuels which can meet the temperature and composition requirements are also suitable. For example, hydrogen, methane and ethylene have been used successfully in the flame plating method of this invention.

Powder velocity in a spray gun of the nature described is roughly proportional to gas velocity. Since thei supply pressure is the primary determinant of gas velocity, the pressure which can be used becomes an important factor in selection of a fuel. The higher the supply pressure capable of being used with a particular fuel, the higher the attainable powder velocity. Higher powder velocities effectively add thermal energy to the powder. This results from the increased temperature rise upon release of kinetic energy on, impact of the powder against the workpiece surface. Thus, fuels permitting highersupply'pressures and higher powder velocitis'rnay have lower flame temperatures and yet still be practical inthe practice of the flame plating method of this invention. r

The hardness and porosity of the coating are dependent to a considerable extent upon powder velocity. This is shown in the following table obtained by'spraying tungsten-carbide-cobalt alloy with a gun employing a throat apparent whenever a non-porous, well-bonded coating is desired. These benefits are not limited to any particular coating material, for although the invention is especially adapted for coating with materials of high melting points, it is also adapted for coating surfaces with any of a wide variety of metals, alloys, metallic compounds, plastics, ceramics and minerals. Base surfaces, which may be precleaned in any suitable manner, may also be of a wide variety of materials. The following table shows several illustrative examples of substances which have been platedby this. process. Generally theplatingswere made using 600 cubic feet perhour of oxygen and acetylene in a burner of the type shown in Fig. l. An oxy acetyl'ene ratio of 1.0 to 1.6 was employed. ,In the case of the copper powder, only 300 cubic feet per hour of oxygen .form non-porous coating can relative to the workpiece.

were made in Plating Adherence 1 5 Workpiece Powder Fair.

Aluminum Nickel Silicon (-200 mesh) Silver Tungsten +12% 00 (-325 mesh Tungsen carbide +23% 00 (-3 ml- Do.

cron Tungsten carbide +12% Ni Do.

micron). Tungsten carbide +20% Ag (-20 Do. 15

micron). t Chromium carbide +15% Ni (-10 Excellent.

micron). Copper .7 Tungsten carbide +8% 00 Fair. Stainless Steel Tungsten carbide +8% 00 (-325 Good mesh).

l The ratings of adherence were made as follows: Fairoxamination of cr ss-secti ned specimens showed a fissure at some point between the plating and the base metal; Goodblack inclusions were observed at the base-plating interface in cross-sectioned specimens, although otherwise adherence seemed to be tight; Excellent-bonding of plating to base metal good, with very few or no inclusions at the interface.

An example of the performance of the present invention is its capacity for depositing a substantially nonporous coating of a high melting point, abrasive-resistant hard material such as tungsten carbide compositions. Using a spray gun of the type shown in Figure l, a tungsten-carbon-cobalt composition containing about 4% carbon and 9% cobalt, in a finely divided powder of the order of 325 mesh was fed into the burner of the gun at a rate of 15 pounds per hour in a hydrogen carrier gas of 60 cubic feet per hour. Acetylene and oxygen at p. s. i. g. were fed to the burner in a ratio of 1.4 cubic feet of the latter to 1 cubic feet of the former at a combined rate of 600 cubic feet per hour. The workpiece, a cylindrical steel piece /2 inch in diameter and 1 /2 inches in length was rotated at 150 revolutions per minute and advanced Vs inch per revolution past the burner outlet, with a standoff distance of 4 inches. In this way the workpiece was coated with a thickness (on the radius) of 0.004 inch in about five seconds. The coated sample was ground and polished by known procedures to a very smooth finish, the hardness of the surface being measured at 1200 Knoop. The gun employed had a water-cooled cylindrical nozzle inch inside diameter by 8 inches long.

The continuous nature of the present invention makes it possible to apply a steady stream of coating particles against a surface with substantially uniform forces imparted to the particles at all times. In this way, a unibe spread over a surface in a relatively short period of operation.

In practice, the gun may be held in either a horizontal or vertical position, and the workpiece to be coated may be moved relative to the gun or the gun may be moved Moreover, in the plating of certain types of work, for example plug gages, the workpiece can be held and rotated in a chuck of the lathe while the gun is moved along the length of the plug. in

,this way, a uniform layer would be deposited on the gage.

It will be understood that the new features of process operation and gun construction herein disclosed may be employed in ways and forms different from those of the preferred embodiments described above, without depart ing from the spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

1. A method of applying a surface coating to an object which comprises introducing a solid coating material and a fluid combustible mixture under pressure into a confined combustion space, heating at least a portion of the coating particles to a high temperature by burning the fluid combustible mixture in said space in the presence of such material, and thereafter propelling heated coating particles toward the surface of the object to be coated at a linear velocity greater than 500 feet per second by discharging the particle-carrying burning gases through a confined path in which such gases are accelerated to an exit velocity sufficiently high to impart such linear velocity to the particles.

2. A method as described in claim 1, wherein said solid coating material is in comminuted form.

3. A method as described in claim 1, wherein said solid coating material is in the form of a rod.

4. A method of applying a surface coating to an object which comprises introducing a solid coating material and a fluid combustible mixture under pressure into a confined combustion space, heating at least a portion of the coating particles to a high temperature by burning of fluid combustible mixture in said space in the presence of such particles, and thereafter propelling heated coating particles toward the surface of the object to be coated in a jet flame having a linear exit velocity greater than 2000 feet per second by discharging the particle-carrying burning gases through a confined path in which such gases are accelerated to such velocity.

5. A method of applying a surface coating to an object which comprises mixing a fluid fuel and a combustion supporting agent to form a combustible mixture, introducing a comminuted solid coating material into said mixture, introducing combustible mixture containing said comminuted solid material into a confined combustion space, heating the coating particles to a high temperature by burning the fluid combustible mixture in said space in the presence of such particles, and thereafter propelling heated coating particles against the surface of the object to be coated in a jet flame having a linear cxit velocity greater than 2,000 feet per second by discharging the particle-carrying burning gases through a confined path in which such gases are accelerated to such velocity.

6. A method of applying a surface coating to an object which comprises mixing a fluid fuel containing a cornminuted solid coating material with a combustion supporting agent to form a combustible mixture, introducing combustible mixture containing said comminuted solid material into a confined combustion space, heating the coating particles to a high temperature by burning the fluid combustible mixture in said space in the presence of such particles, and thereafter propelling heated coating particles against the surface of the object to be coated in a jet flame having a linear exit velocity greater than 2,000 feet per second by discharging the particle-carrying burning gases through a confined path in which such gases are accelerated to such velocity.

7. A method of applying a surface coating to an object which comprises mixing a fluid fuel with a combustion. supporting agent containing comminuted solid coating material to form a combustible mixture, introducing combustible mixture containing said comminuted solid material into a confined combustion space, heating the coating particles to a high temperature by burning the fluid combustible mixture in said space in the presence of such particles, and thereafter propelling heated coating particles against the surface of the object to be coated in a jet flame having a linear exit velocity greater than 2,000 feet per second by discharging the particle-carrying burning gases through a confined path in which such gases are accelerated to such velocity.

8. A method of applying a surface coating to an object which comprises mixing a fluid fuel and a combustion supporting fluid to form a combustible mixture, introducing a carrier fluid containing comminuted solid coating material into one of such fluids prior to mixing, introducing combustible mixture containing comminuted solid material into a confined combustion space, heating the coating particles to a high temperature by burning the fluid combustible in said space in the presence of such particles, and thereafter propelling heated coating particles against the surface of the object to be coated in a jet flame having a linear exit velocity greater than 2,000 feet per second by discharging the particle-carrying burning gases through a confined path in which such gases are accelerated to such velocity.

9. A method of applying a surface coating to an object which comprises continuously introducing a fluid combustible mixture under pressure and a solid coating mate rial into a throat combustion burner wherein combustion of the mixture takes place in the presence of the coating material, passing the burning gases containing coating particles through said burner, discharging particle-carrying burning gases from the burner to develop substantial force for transmission to the particles so as to eject them in a jet flame having a high flame intensity and a high mass velocity, and directing said flame toward the surface to be coated so as to propel heated coating particles at a high linear velocity against such surface to deposit there and build up a coating.

10. A method of applying a surface coating of a high melting point metal composition to an object which comprises suspending such metal composition in finely divided form in a fluid combustible mixture containing oxygen and fuel in proportions to provide upon combustion a non-oxidizing flame, introducing the particle-carrying fluid combustible mixture under pressure into a confined combustion space, heating the coating particles to a high temperature by burning the fluid combustible mixture in said space in the presence of such particles, and thereafter propelling heated coating particles against the surface of the object to be coated in a jet flame having a linear exit velocity greater than 2,000 feet per second by discharging the particle-carrying burning gases in a confined path in which such gases are accelerated to such velocity.

11. A method of applying a surface coating to an object which comprises concomitantly introducing a solid coating material and a fluid combustible mixture under pressure into an internal combustion zone from which burning gases are discharged in a jet flame having a linear velocity greater than 2000 feet per second, heating the coating material to a high temperature by burning the fluid combustible mixture in said zone in the presence of such coating material, and directing the flame toward the surface of the object to be coated to propel heated coating particles ejected by and in the flame onto such surface.

12. A flame-spray gun for applying surface coatings to objects, comprising a-hollow member defining at least along a portion of its length a throat combustion chamber said chamber having an inlet at one end and an outlet at its other end and a side wall which is continuous from inlet to outlet, said chamber having an entrance portion in which fuel and oxygen under pressure are mixed and combustion is initiated, passage means for supplying fluid fuel and oxygen to said entrance portion of the throat combustion chamber, means for introducing solid coating material into the combustion chamber, said throat combustion chamber having an outlet at least .02 inch in diameter downstream of said entrance por tion for discharging coating-particle-carrying burning gases in a jet flame, and said throat combustion chamber extending from said entrance portion to said outlet without constriction in cross-sectional area.

13. A method of applying a surface coating of a metal carbide composition to an object which comprises suspending said composition in finely divided form in a fluid combustible mixture containing oxygen and fuel in proportions to provide upon combustion a non-oxidizing flame and less than 67 percent oxidants in the burning gases, introducing the particle-carrying fluid combustible mixture under pressure into a confined combustion space, heating the coating particles to a high temperature by burning the fluid combustible mixture in said space in the presence of such particles, and thereafter projecting heated coating particles against the surface of the object to be coated at at least their flowing temperature by discharging the particle-carrying burning gases in a confined path in which such gases are accelerated to an exit velocity imparting sufficient kinetic energy to the particle so that, together with their thermal energy, the particles will be at least at such flowing temperature upon impact.

14. A method of applying a surface coating of a tungsten carbide composition to an object which comprises suspending said tungsten carbide composition divided to a powder finer than 325 mesh in a fluid combustible mixture containing oxygen and acetylene in a ratio between 08:1 and 1.9:1, introducing the particlecarrying fluid combustible mixture under pressure into a confined combustion space, heating the coating particles to a high temperature by burning the fluid combustible mixture in said space in the presence of such particles, and thereafter projecting heated coating particles against the surface of the object to be coated at at least their flowing temperature by discharging the particlecarrying burning gases in a confined path in which such gases are accelerated to an exit velocity imparting sufficient kinetic energy to the particles so that, together with their thermal energy, the particles will be at least at such flowing temperature upon impact.

15. A flame spray gun comprising a hollow member having at least along a portion of its length an internal combustion throat passage defined by walls extending from an inlet zone at one end to an outlet at its other end, said passage extending from the inlet zone to the outlet without constriction in cross-sectional area and being at least .02 inch in diameter downstream of said inlet zone, means for supplying fluid combustible to said inlet zone comprising first and second conduits supplying fluid fuel and fluid oxidant each under pressure, said conduits terminating respectively in delivery orifices disposed adjacent each other and said inlet zone on the upstream side thereof, said delivery orifices being arranged for delivering the oxidant and fuel streams to intersect at a substantial angle to each other for rapid mixing and combustion in said throat passage; and means for introducing solid material into said internal combustion throat passage wherein the material is heated to a high temperature and particle carrying burning gases are discharged from the outlet in a jet flame.

16. A flame spray gun according to claim 15 in which said means for introducing solid material comprises means for feeding a comminuted solid material with one of said oxidant and fuel gas streams to said inlet zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,137,442 Callan Nov. 22, 1938 2,659,623 Wilson Nov. 17, 1953 2,714,563 Poorman Apr. 2, 1955 

1. A METHOD OF APPLYING A SURFACE COATING TO AN OBJECT WHICH COMPRISES INTRODUCING A SOLID COATING MATERIAL AND A FLUID COMBUSTIBLE MIXTURE UNDER PRESSURE INTO A CONFINED COMBUSTION SPACE, HEATING AT LEAST A PORTION OF THE COATING PARTICLES TO A HIGH TEMPERATURE BY BURNING THE FLUID COMBUSTIBLE MIXTURE IN SAID SPACE IN THE PRESENCE OF SUCH MATERIAL, AND THEREAFTER PROPELLING HEATED COATING PARTICLES TOWARD THE SURFACE OF THE OBJECT TO BE COATED AT A LINEAR VELOCITY GREATER THAN 500 FEET PER SECOND BY DISCHARGING THE PARTICLE-CARRYING BURNING GASES THROUGH A CONFINED PATH IN WHICH SUCH GASES ARE ACCELERATED TO AN EXIT VELOCITY SUFFICIENTLY HIGH TO IMPART SUCH LINEAR VELOCITY TO THE PARTICLES. 